Target tracking sight

ABSTRACT

The invention relates to a sighting device, in particular an optical sighting device, for target tracking purposes. The sight comprises a sight casing, which is manually movable by a sight operator in azimuth as well as in elevation, and optical sighting means mounted in said sight casing and having a line of sight which can be deviated in azimuth as well as in elevation relative to the sight casing under the control of the sight operator and which is gyro-stabilized so as to be independent of any movements of the sight casing. During the target catching phase and the rough-aiming of the sight line on the target, however, the gyrostabilization of the sight line can be suspended and the sight line be locked in a predetermined fixed position relative to the sight casing so as to be movable in space only by rotation of the sight casing. Special features of the sight guarantee that, when said locking of the sight line relative to the sight casing is released and the gyro-stabilization of the sight line is reestablished, the sight line will automatically continue to move in substantially the same direction and with substantially the same angular velocity relative to space as immediately before the transition from a sight line stationarily locked relative to the sight casing to a gyro-stabilized sight line which the sight operator can deviate relative to the sight casing and which is independent of the motions of the sight casing.

United States Patent 'Borjeson [451 Oct. 10, 1972 [54] TARGET TRACKING SIGHT [72] Inventor: Jan Lennart Borjeson, Kalskoga,

Sweden [73] Assignee: Aktiebolaget Bofors, Bofors, Sweden 22 Filed: Feb. 26, 1971 21 Appl.N0.: 119,208

[30] Foreign Application Priority Data March 6, 1970 Sweden ..3047/70 [52] U.S. Cl. ..3l8/649, 318/582, 318/640 [51 1 Int. Cl ..B64c 17/02 [58] Field of Search ..3l8/648, 649, 640, 591, 582

[56] References Cited UNlTED STATES PATENTS 2,700,106 l/1955 Taylor ..3l8/649 3,443,476- 5/1969 Heider et a1. ..318/649 X 3,471,108 10/1969 Corso ..3l8/649X Primary ExamineriBenjamin Dobeck Attorney-Hane, Baxley & Spiecens [57] ABSTRACT The invention relates to a sighting device, in particular an optical sighting device, for target tracking purposes. The sight comprises a sight casing, which is manually movable by a sight operator in azimuth as well as in elevation, and optical sighting means mounted in said sight casing and having a line of sight which can be deviated in azimuth as well as in-elevation relative to the sight casing under the control of the sight operator and which is gyro-stabilized so as to be independent of any movements of the sight casing. During the target catching phase and the rough-aiming of the sight line on the target, however, the gyro-stabilization of the sight line can be suspended and the sight line be locked in a predetermined fixed position relative to the sight casing so as to be movable in space only by rotation of the sight casing. Special features of the sight guarantee that, when said locking of the sight line relative to the sight casing is released and the gyro-stabilization of the sight line is reestablished, the sight line will automatically continue to move in substantially the same direction and with substantially the same angular velocity relative to space as immediately before the transition from a sight line stationarily locked relative to the sight casing to a gyro-stabilized sight line which the sight operator can deviate relative to the sight casing and which is independent of the motions of the sight casing.

5 Claims, 3 Drawing Figures PATENTEDucI 10 me '5 FIG. 2

FIG. 3

TARGET TRACKING SIGHT The present invention relates to sighting devices, in particular optical sighting devices, for target tracking, which have a gyro-stabilized line of sight having a direction in space, which can be moved by the sight operator during the target tracking operation, e.g., by means of a control lever manually actuated by the sight operator. A sight of the type, to which the invention is related, comprises a member which is movably mounted in a sight casing and which determines the direction of the sight line relative to the sight casing. In an optical sight, for instance, said member may be a mirror which is rotatable about two mutually orthogonal axes. This member is coupled to a gyroplatform whichis rotatable in the sight casing about two mutually orthogonal axes corresponding to the azimuth deflection axis and the elevation deflection axis of the sight line and which carries two angular velocity responsive gyros mounted on the gyro-platform so as to be responsive to the angular velocities of the gyro-platform about its two axes of rotation and to produce signals proportional thereto, which areapplied as negative feedback signals to servomotors coupled to the gyro-platform about said two axes. With this arrangement the line of sight will be gyro-stabilized so that its direction in space remains unaffected of any movements of the sight casing. Furthermore, the sight is provided with two signal generators, which are manually actuated by the sight operator, e.g., by means of a control lever, and which produce control signals corresponding to the displacement of said control lever in two mutually orthogonal directions, these control signals being applied to the servomotors coupled to the gyro-platform, whereby the attitude of the gyro-platform and thus the direction of the sight line relative to space can be varied by use of the control lever.

Due to the mechanical structure of the sight and the geometric restriction of the viewing window in the front wall of the sight casing, through which the line of sight must pass, the direction of the sight line relative to the sight casing can only be varied within a limited solid angle. Therefore, in a sighting device of this type also the sight casing must be movable in azimuth and elevation so that it is possible for the sight operator, when tracking a target by moving the sight line relativeto space, to follow along with the sight casing so that the sight line remains within the viewing window of the sight casing. Due to the gyro-stabilization of the sight line, however, the movements of the sight casing will not affect the direction of the sight line, which is controlled entirely by means of the control lever.

When catching a target with the sight before the actual target tracking operation, however, very large and rapid variations of the direction of the sight line may be necessary, wherefore during this target catching phase it is less advantageous to have the sight line stabilized and to move it towards the target by means of the control lever controlling the servomotors of the gyro platform and at the same time to follow along at substantially the same speed with the sight casing. In particular this is of course the case, if during the target catching phase an auxiliary sighting means on the sight casing, as

for instance a dioptic, is used which gives the sight operator a larger field of view than the gyro-stabilized sighting means used for the subsequent accurate target tracking operation. In accordance with the present invention this problem may be solved in that the sighting device is provided with means for locking the gyro-platform and thus also the sight line in a predetermined fixed position relative to the sight casing so that the sight operator can carry out the target catching operation with the sight line locked relative to the sight casing and thus by rotation of the sight casing only without any control of the sight line by means of the control lever. When in this way the sight operator has caught the target and moved the sight line to be directed substantially on the target, he can release the locking of the gyro-platform and thus of the sight line so that this becomes gyro-stabilized and subsequently proceed with the more accurate target tracking by' controlling the sight line by means of the control lever.

Such a locking of the gyro-platform and thus of the sight line relative to the sight casing during the initial target catching operation produces a serious problem, however, when the sight operator after the target catching phase releases the locking of the sight line and shall proceed to track the target more accurately by controlling the sight line by means of the control lever. This problem is due to the fact that at the end of the target catching phase the sight operator has obviously given the sight casing and the sight line locked thereto a direction of movement and an angular velocity substantially corresponding to the direction of movement and the angular velocity of the target being tracked. When the sight operator now releases the locking of the gyroplatform and thus of the sight line in order to proceed with a more accurate target tracking with a gyro-stabilized sight line, the gyro-stabilization of the sight line will stop the sight line substantially instantaneously in the direction it had when the locking of the gyro-platform was released by the sight operator. The target, however, will of course continue to move with substantially unchanged speed and in unchanged direction and the sight operator will also automatically continue to move the sight casing substantially in the same direction and substantially with the same speed as at the end of the target catching operation. The automatic and unavoidable result hereof will be that the sight will lose the target and it may easily occur that the deviation between the direction to the target and the direction of the now gyro-stabilized sight line will increase to such a value, before the sight operator has managed to correct the direction of the sight line by actuation of the control lever, that the target is no longer within the field of view of the sight operator through the sighting device. In such a case the sight operator will be forced to carry out a renewed target catching operation.

The object of the present invention is therefore to provide a sighting device of the type described in the foregoing, in which the problems discussed above during the target catching phase and at the transition from the target catching phase to the more accurate target tracking phase with a gyro-stabilized sight line are eliminated.

In accordance with the invention this is achieved in that the sight is provided with locking means for temporarily locking the gyro-platform and thus'the sight line in a predetermined fixed position relative to the sight casing, said locking means including signal storing means and switching means for disconnecting the output signals of the gyros and the manually actuated signal generators from the servomotors of the gyroplatform and instead connecting the output signals of the gyros to said signal storing means when the gyroplatform is locked in said fixed position, and disconnecting the input signals from said signal storing means and reconnecting the output signals of the gyros and of the manually actuated signal generators to the servomotors of the gyro-platform and also connecting the signals stored in said signal storing means to the servomotors of the gyro-platform as additional control signals therefore, when the gyro-platform is released from said fixed position relative to the sight casing.

In a sighting device according to the invention the signal storing means will at the transition from the rough-aiming phase with a locked sight line to the precision-aiming phase with a gyro-stabilized sight line contain stored signals representing the angular velocities in azimuth and elevation of the sight line and thus of the target at the end of the rough-aiming and by the application of these stored signals as additional control signals to the servomotors of the gyro-platform, when the gyro-platform is released, the now gyro-stabilized sight line is automatically caused to continue to move with the same angular velocities and in the same direction as at the end of the preceding rough-aiming phase with a locked sight line and will consequently substantially follow the moving target without any actuation of the control lever by the sight operator being necessary. As a consequence, there is no risk of losing the target at the transition from the rough-aiming phase with a locked sight line to the precision-aiming phase with a gyro-stabilized sight line and the sight operator can focus his whole attention on aiming the sight line still more accurately on the target by means of the control lever.

The signal storing means are preferably such that they have a declining storing characteristic after the disconnection of the input signals so that the stored signals, which after the release of the locking of the gyro-platform are applied to the servomotors orthe gyro-platform as additional control signals therefore, decrease in accordance with a predetermined function of time. Consequently, the effect of these stored additional control signals will gradually fade and vanish after a predetermined time, but under this time it is an easy matter for the sight operator to replace them to a required extent with corresponding control signals generated by the signal generators actuated by the control lever.

The locking of the gyro-platform and thus the sight line relative to the sight casing can be obtained in various ways. Thus, for instance, mechanical locking means can be used. Electric locking means are, however, to be preferred. Such electric locking means may preferably comprise two signal generators coupled to the axes of the gyro-platform for generating signals representing the angular position of the gyro-platform about its axes relative to the sight casing, which signals are applied by the switching means of the locking device to the servomotors of the gyro-platform as control signals therefore when the platform is to be locked.

In the following the invention will be further described with reference to the accompanying drawing,

which illustrates by way of example an embodiment of the invention. In the drawings FIG. 1 shows schematically and in vertical section a sighting device embodying the invention;

FIG. 2 shows a portion of the sighting device in FIG. 1 as seen from the line ll II in FIG. 1; and

FIG. 3 is a simplified diagram of the electric circuits for the gyro-stabilization and the control of the sight line by means of a control lever and for the locking of the sight line relative to the sight casing, the drawing showing only the circuits related to the control of the sight line in azimuth, as the circuits for the control of the sight line in elevation are designed in identically the same manner.

The aiming sight shown schematically in the drawing includes a sight casing l, which is mounted on a schematically indicated stand 2 so as to be rotatable in elevation as well as azimuth. The front wall of the sight casing is provided with a viewing window or sight opening 3. A telescope optics including in conventional manner an objective 4, a prism 5 and an eye-piece 6 has a fixed mounting in the sight casing 1. In front of the eye-piece 6 a hairline cross or a similar device 7 is mounted, by means of which the sight operator can determine the deviation between the sight line and a target viewed through the sighting telescope. An oblique mirror 8 is disposed between the telescope objective 4 and the viewing window 3 so as to deflect the sight line of the telescope out through the viewing window 3. Consequently, the direction of the exit sight line 9 is determined by the mirror 8, which is universally pivoted in the sight casing 1 so that the direction of the exit sight line 9 can be moved in azimuth as well as elevation by variation of the attitude of the mirror 8.

For this purpose the mirror 8 is pivoted about an axis H I-I (compare FIG. 2) in a gimbal 10, which is pivoted about an axis S S in the bottom of the sight casing and a bracket 11 projecting from the front wall of the sight casing 1. By rotation of the gimbal 10 about the axis S S the direction of the sight line 9 can be changed in azimuth, whereas by rotation of the mirror 8 about the axis I-I H the direction of the sight line 9 can be changed in elevation.

For the gyro-stabilization and the control of the mirror 8 and thus of the sight line 9 a gyro-platform 12 is mounted in the gimbal 10 so as to be rotatable relative thereto about an axis 13, which is parallel to the pivot axis H H of the mirror 8. This gyro-platform 12 carries two angular velocity responsive gyros G, and G,,. The gyro G, is mounted on the platform so as to be responsive to the angular velocity of the platform 12 about the axis S S, whereas the gyro G,, is mounted on the platform so as to be responsive to the angular velocity of the platform 12 about its axis 13. The gyros generate signals proportional to said angular velocities. A servomotor M mounted on the gimbal 10 is coupled to the axis 13 of the gyro-platform 12, whereas the servomotor M, supported by the sight casing 1 is coupled to the axis S S of the gimbal 10. For the gyro-stabilization of the platform 12 in space the output signal of the gyro G, is in conventional manner applied as a negative feedback signal to the servomotor M, whereas the output signal of the gyro G,, is applied as a negative feedback signal to the servomotor M,,. As the mirror 8 is supported in the same gimbal 10 as the gyroplatform 12, the stabilization of the gyro-platform 12 about its axis S S produces automatically a corresponding stabilization of the mirror 8 and thus of the sight line 9 about the axis S S. As illustrated in FIG. 1, the gyro-platform 12 is additionally coupled to the mirror 8 through a stiff rod 14, which has its one end attached to the rear side of the platform 12, and a stiff rod 15, which has its one end attached to the rear side of the mirror 8. The opposite end of the rod 14 is provided with a pin 14a which is movable in the forkshaped end 15a of the rod 15. The effective length of the rod 14 from the pivot center of the gyro-platform 12 to the pin 14a is equal to the distance between the pivot .center of the platform 12 and the pivot center of the mirror 8. It is appreciated that this mechanical coupling between the gyro-platform l2 and the mirror 8 causes that any angular rotation of the platform about its axis 13 results in an exactly equally large angular rotation of the sight line 9 about the axis H H. The stabilization of the gyro-platform 12 about its axis 13 produces consequently a corresponding stabilization of the mirror 8 and thus of the sight line 9 about the axis H H.

For the control and variation of the direction of the gyro-stabilized sight line 9 a control lever or joy-stick 16 is mounted on the lower side of the sight casing 1. The joystick 16 is universally pivoted so as to be movable in two mutually orthogonal directions and is coupled to two signal generators S, and S,, in such a manner that the signal generator S, generates a signal corresponding to the displacement of the joystick 16 in the one of said two directions, whereas the second signal generator 8,, generates a signal representing the displacement of the joystick 16 in the other one of said two directions. The output signals from the signal generators S, and 8,, can be connected as control signals to the servomotors M, and M,,, respectively, whereby the attitude of the gyro-platform 12 in space and thus the direction of the sight line 9 in space can be changed in azimuth as well as elevation by means of the joystick 16. A handle 17 is mounted on the lower side of the sight casing l in front of the joystick 16. This handle can be used by the sight operator for rotation of the sight casing 1 in azimuth and elevation.

Further, an electric signal generator P,, for instance consisting of a potentiometer, is coupled to the axis S S of the gimbal 10 and generates an output signal representing the angular position of the gimbal 10 and thus of the gyro-platform l2 and the sight line 9 about the axis S S relative to the sight casing 1. In similar manner a signal generator P,, is coupled to the axis 13 of the gyro-platform l2 and produces an output signal representing the angular position of the gyro-platform 12 and thus of the sight line 9 in elevation relative to the sight casing 1. As will be described more in detail in the following, these two signal generators P, and P,, are used for the locking of the gyro-platform l2 and thus of the sight line 9 in a predetermined position relative to the sight casing 1.

The electric circuits in the stabilizing, control and locking system of the sight are shown schematically in FIG. 3, which shows, however, only the circuits related to the stabilization, the control and locking, respectively, of the sight line 9 in azimuth, as the corresponding circuits for elevation are designed in exactly the same way.

Thus, FIG. 3 shows the gyro-platform 12, which is pivoted in the sight casing 1 about the axis S S and which carries the angular velocity responsive gyro G The servomotor M and the signal generator P, are coupled to the gyro-platform 12 about its axis S S. The servomotor M, is controlled by the output signal from an amplifier F 1 having its input connected to a throwover switch K1. Consequently, the servomotor M, can receive as a control signal either the output signal from the signal generator P, or the output signal from an amplifier F2. The output signal of the gyro G, is connected on the one hand to an input of the amplifier F2 and on the other hand through a make-break switch K2 to the input of an amplifier F3. The amplifier F3 has a negative feedback through a resistance and a capacitor 18 connected across its output. The output signal from the amplifier F3 is connected to a second input of the amplifier F2. An additional input of the amplifier F2 receives the output signal from the signal generator S, actuated by the joystick 16.

When the gyro-platform I2 and thus the sight line 9 is to be in a locked position relative to the sight casing, the two switches K1 and K2 are in the positions illustrated in the drawing. The two switches K1 and K2 are mechanically interconnected so as to be operated simultaneously. The switches are preferably manually operated by the sight operator. With the switches K1 and K2 in this locked position the servomotor M is controlled by the output signal from the signal generator P,. The signal generator P, is adapted to generate an output signal, which is zero fora predetermined desired locking position of the gyro-platform 12 and thus the sight line 9 relative to the sight casing 1, and the output signal of the signal generator is fed back to the servomotor M, through the switch K1 and the amplifier Fl with such a polarity that the servomotor M, endeavours to maintain the output signal from the signal generator P, on the value zero, that is to keep the gyro-platform 12 and thus the sight line 9 in the predetermined locking position. At the same time the output signal from the gyro G,, which is proportional to the angular velocity of the gyro-platform 12 and thus the sight line 9 about the axis S S, is supplied on the one hand directly to the input 0 of the amplifier F2 and on the other hand through the closed switch K2 to the amplifier F3. It is appreciated that the amplifier F3 with its negative feedback together with the capacitor 18 connected across the output of the amplifier functions as a signal storing device, which strives to maintain the capacitor 18 charged to a voltage which corresponds exactly to the input voltage on the input of the amplifier F3. Consequently, the signal on the input b of the amplifier F2 has exactly the same amplitude as the signal on the input c of the amplifier, the polarities of these two input signals being opposite, however, wherefore the signals cancel each other. As during the target catching and rough-aiming phase of the operation of the sight, i.e., when the gyro-platform 12 and thus the sight line 9 are locked in the described manner relative to the sight casing 1, the sight operator keeps the joystick 16 in its neutral position, the input signal on the input a of the amplifier F2 from the signal generator S, is also zero.

When the target catching and rough-aiming of the sight on the target is completed, the sight operator releases the locking of the gyro-platform 12 and thus of the sight line 9 in that he switches the throw-over switch K1 to its opposite position and at the same time opens the switch K2. The servomotor M, of the gyroplatform 12 receives now its control signal from the output of the amplifier F2. This amplifier F2 receives on its input b the signal stored by the amplifier F3 in the capacitor 18. As explained in the foregoing this signal corresponds to the output signal of the gyro G, at the moment when the locking of the gyro-platform 12 was released, i.e., it represents the angular velocity of the gyro-platform and thus of the sight line 9 and consequently also of the target about the axis S S at the end of the target catching and rough-aiming phase. Consequently, the servomotor M, will strive to impart on the gyro-platform l2 and thus on the sight line 9 exactly the same angular velocity about the axis S S also after the release of the locking of the gyro-platform and the sight line, without any control signal being produced on the input a of the amplifier F2 by actuation of the joystick 16 and thus of the signal generator S, from the sight operator. Consequently, the removal of the locking of the sight line 9 does not cause any instantaneous change in the direction of movement and angular velocity of the sight line, wherefore the sight operator can concentrate his whole attention on correcting the direction of the sight line 9 still more accurately and adapting the movement of the sight line to the continued movements of the target by the aid of the joystick 16.

The signal stored on the capacitor 18 will gradually decrease at a rate determined by the discharge circuit in which the capacitor 18 is inserted. The discharge rate for the capacitor can without any difficulties be selected so that the sight operator can by means of the joystick 16 change the value of the control signal on the input a of the amplifier F2 at the rate and to the extent necessary for maintaining the sight line 9 on the target.

It is appreciated that during the precision-aiming of the gyro-stabilized platform 12 and thus of the sight line 9 by means of the joystick 16 the output signal from the signal generator P, will always represent the angular position of the gyro-platform 12 and thus of the sight line 9 relative to the sight casing 1 about the axis S S. The output signal of the signal generator P, is therefore connected to a threshold circuit 19 designed to light up a first indicator lamp 20, if the output signal from the signal generator P, exceeds a predetermined maximum positive value, and to light up a second indicator lamp 21, if the output signal from the signal generator P, exceeds a predetermined negative value. Consequently, the two indicator lamps 20 and 21 can be used for indicating to the sight operator that the direction of the sight line 9 relative to the sight casing l approaches the limit of the viewing window 3 in the sight casing, wherefore the sight operator has to follow along with the sight casing l. The two indicator lamps 20 and 21 may, preferably, be reflected into the field of view of the sight operator, whereby he will automatically be informed when and in which direction he has to follow along with the sight casing 1.

It should be noticed that the embodiment of the invention illustrated in the enclosed drawings and described in the foregoing is only an illustrative example of the invention and that several other embodiments of the invention are possible. As already mentioned in the foregoing it would be possible, instead of the electrical locking of the gyro-platform 12 and thus of the sight line 9 illustrated in FIG. 3, to use a purely mechanical locking of the gyro-platform and the sight line. Further, in the circuit diagram shown by way of example in FIG. 3, the control signal from the control signal generator S, is connected directly to the servomotor M, through the amplifiers F1 and F2. in the practice, however, the control signals produced by means of the joystick 16 are generally passed through signal modifying networks giving a predetermined desired control function, i.e., a predetermined desired relationship between the movements of the joystick 16 and the movements of the sight line 9.

Although in the foregoing the invention has been described with reference to an aiming sight having a sight line which is movable in azimuth as well as in elevation, it is appreciated that the invention can, of course, be used also in an aiming sight having a sight line, which is movable only in one direction, e.g'., in elevation or in azimuth.

lclaim:

1. A sighting device for target tracking, comprising a sight casing (1) movable in azimuth and elevation, a movable member (8) in said sight casing for determining the direction of the line of sight (9) relative to the sight casing, a gyro-platform (12) mounted in said sight casing so as to be rotatable thereto about two mutually orthogonal axes (S S, 13) corresponding to the azimuth axis and the elevation axis, respectively, of the sight line (9), two angular velocity responsive gyros (6,, G,,) mounted on said gyro-platform so as to be responsive to the angular velocities thereof about said two axes and to generate signals proportional to said angular velocities, servomotors (M,, M,,) coupled to said gyro-platform for rotation thereof about said two axes, said signals from said gyros being connected to said servomotors as negative feedback signals, and manually actuated signal generators (8,, S,,) for generating control signals for said servomotors for variation of the attitude of said gyro-platform and thus the direction of said sight line relative to space, characterized by locking means for temporarily locking said gyro-platform ('12) and thus said sight line (9) in a predetermined fixed position relative to said sight casing (1), said locking means including signal storing means (F3, 18) and switching means (K1, K2) for disconnecting the output signal of said gyros ((3,, 6,.) and of said manually actuated signal generators (8,, S,,) from said servomotors (M,, M,,) for said gyro-platform (l2) and connecting the output signals of said gyros to said signal storing means (F3, 18), when said gyro-platform (12) and thus said sight line (9) are locked in said predetermined fixed position relative to said sight casing (1), and respectively disconnecting the input signals to said signal storing means and reconnecting the output signals of said gyros and said manually actuated signal generators to said servomotors and additionally connecting the signals stored in said signal storing means to said servomotors as additional control signals therefore, when. said gyro-platform (12) and thus said sight line (9) are released from said predetermined fixed position elative to the sight casing (l 2. A sighting device as claimed in claim 1, wherein said locking means include two signal generators (P,,

P,,) coupled to said gyro-platform (12) about said two axes (S S, 13) for generating signals representing the angular position of said gyro-platform about said axes relative to the sight casing (1), said switching means including means (K1) for connecting said signals to said servomotors (M,, M,,) as control signals therefore, when said gyro-platform (l2) and thus said sight line (9) is to be locked in said predetermined position relative to the sight casing.

3. A sighting device as claimed in claim 2, comprising signal threshold responsive means (19) receiving the output signals from said signal generators (P,, P,,) coupled to said gyro-platform (12) for indicating when said signals'exceed a predetermined maximum value.

4. A sighting device as claimed in claim 1, wherein said signal storing means (F3 18) have a declining storing characteristic after disconnection of their input signals, whereby the stored signals decrease in accordance with a predetermined function of time.

5. A sighting device as claimed in claim 4, wherein said signal storing means include an amplifier (F3) with a negative feedback and a capacitor (18) connected across the output of said amplifier for each signal to be stored. 

1. A sighting device for target tracking, comprising a sight casing (1) movable in azimuth and elevation, a movable member (8) in said sight casing for determining the direction of the line of sight (9) relative to the sight casing, a gyro-platform (12) mounted in said sight casing so as to be rotatable thereto about two mutually orthogonal axes (S - S, 13) corresponding to the azimuth axis and the elevation axis, respectively, of the sight line (9), two angular velocity responsive gyros (Gs, Gh) mounted on said gyro-platform so as to be responsive to the angular velocities thereof about said two axes and to generate signals proportional to said angular velocities, servomotors (Ms, Mh) coupled to said gyro-platform for rotation thereof about said two axes, said signals from said gyros being connected to said servomotors as negative feedback signals, and manually actuated signal generators (Ss, Sh) for generating control signals for said servomotors for variation of the attitude of said gyroplatform and thus the direction of said sight line relative to space, characterized by locking means for temporarily locking said gyro-platform (12) and thus said sight line (9) in a predetermined fixed position relative to said sight casing (1), said locking means including signal storing means (F3, 18) and switching means (K1, K2) for disconnecting the output signal of said gyros (Gs, Gh) and of said manually actuated signal generators (Ss, Sh) from said servomotors (Ms, Mh) for said gyroplatform (12) and connecting the output signals of said gyros to said signal storing means (F3, 18), when said gyro-platform (12) and thus said sight line (9) are locked in said predetermined fixed position relative to said sight casing (1), and respectively disconnecting the input signals to said signal storing means and reconnecting the output signals of said gyros and said manually actuated signal generators to said servomotors and additionally connecting the signals stored in said signal storing means to said servomotors as additional control signals therefore, when said gyro-platform (12) and thus said sight line (9) are released from said predetermined fixed position elative to the sight casing (1).
 2. A sighting device as claimed in claim 1, wherein said locking means include two signal generators (Ps, Ph) coupled to said gyro-platform (12) about said two axes (S - S, 13) for generating signals representing the angular position of said gyro-platform about said axes relative to the sight casing (1), said switching means including means (K1) for connecting said signals to said servomotors (Ms, Mh) as control signals therefore, when said gyro-platform (12) and thus said sight line (9) is to be locked in said predetermined position relative to the sight casing.
 3. A sighting device as claimed in claim 2, comprising signal threshold responsive means (19) receiving the output signals from said signal generators (Ps, Ph) coupled to said gyro-platform (12) for indicating when said signals exceed a predetermined maximum value.
 4. A sighting device as claimed in claim 1, wherein said signal storing means (F3 18) have a declining storing characteristic after disconnection of their input signals, whereby the stored signals decrease in accordance with a predetermined function of time.
 5. A sighting device as claimed in claim 4, wherein said signal storing means include an amplifier (F3) with a negative feedback and a capacitor (18) connected across the output of said amplifier for each signal to be stored. 